This invention relates to a dielectric resonator filter and, more particularly, to a resonator filter constructed with a thermally conductive, electrically insulating support for a resonator, and including a locating of tuning screws behind a resonator to accommodate increased electromagnetic field strength and power.
A dielectric resonator filter constructed of a series of dielectric resonators enclosed within metallic cavities is employed in situations requiring reduced physical size and weight of the filter. One such situation of interest is in a satellite communication system wherein such a filter is to be carried on board the satellite as a part of microwave circuitry. The reduced size of such a filter arises because the wavelength of an electromagnetic signal within a dielectric resonator is substantially smaller than the wavelength of the same electromagnetic signal in vacuum or in air. Coupling of electromagnetic power between contiguous cavities may be accomplished by means of slotted irises, as is disclosed in Fiedziuszko, U.S. Pat. No. 4,489,293, this patent describing the construction and tuning of a multiple, dielectric-loaded, cavity filter.
A problem arises in the construction of such a filter in that the tuning screws are supported by the cavity sidewalls at positions facing sidewalls of the resonators, and extend radially inward of the cavity sidewalls providing a gap between the tip of each screw and its respective resonator. Such a gap may support an electric arc in the case of elevated microwave power and, therefore, serves to limit the amount of power which can be handled by the filter. Furthermore, presently available supports which support the resonators within their respective cavities are limited in their capacity to withdraw heat from the resonators. Since increased microwave power results in increased dissipation of heat within a resonator, the resonator may become so hot as to alter its microwave characteristics resulting in degradation of the filter response. Therefore, the limited thermal conductivity of present resonator supports also serves as a limitation on the power handling capability of the filter.